Speakers are generally classified as one of two types: dynamic speakers and crystal speakers utilizing a piezo-electric element.
The dynamic speaker is composed of a magnetic circuit, a voice coil and cone paper. Dynamic speakers are widely used due to their simple structure and high modulation characteristics.
However, there are also several drawbacks attributed to the large size and heavy weight of dynamic speakers. Recently, crystal speakers were developed which removed such drawbacks. In crystal speakers, the piezo-electric element transduces electric signals into sound signals. When voltage is supplied to the piezo-electric element, mechanical vibration occurs. This is delivered to the diaphragm which then generates the sound wave. Crystal speakers are smaller and lighter than dynamic speakers, are convenient to use and possess the advantages of easy assembly and mass production.
However, since the sound pressure characteristic of the piezo-electric element belongs to the high level sound range, crystal speakers are not suitable for reproducing medium or low level sounds. This drawback restricts the use of crystal speakers to only tweeters for high level sounds.
In this respect, the present invention provides a film speaker which is composed of a piezo-electric element and a film diaphragm in order to eliminate the above-mentioned problems of prior art speakers and to achieve a wider range of sound pressure characteristics. It also provides improvements in the position of the film diaphragm and the piezo-electric element, so that the film speaker can produce better quality sound pressure characteristics.